Not applicable.
(1) Field of the Invention
This invention generally relates to navigational systems and more specifically to the generation of a route with intermediate way points that avoid predetermined areas.
(2) Description of the Prior Art
A number of navigation systems exist that have the capability of plotting a course from an initial point to a destination. Often times these courses involve individual paths or legs to intermediate way points. Many of these systems take into account various terrain features in plotting such a course and locating particular way points.
For example, U.S. Pat. No. 4,812,990 (1989) to Adams et al. discloses a system and method for determining the optimal path for an aircraft. A two-dimensional reference grid is constructed so that a first position is in the center of a first rank of the grid and a second position is adjacent to the center cell of the last rank. Dynamic programming techniques enable the determination of possible flight paths between the first and second positions and the selection of a path of minimum cost. Possible flight paths are constructed by identifying possible connections between the last rank and the second position and then between each pair of adjacent ranks, working backward from the last rank to the first position in the first rank. A possible connection is deemed to exist when an aircraft can fly from one point to a target point, as between specified cells and adjacent ranks, and arrive at the target point within particular heading limits without exceeding a predetermined maximum lateral exhilaration of the aircraft. Corresponding heading limits are determined for each connected cell on the grid so that all possible flight paths are examined consistent with preselected heading limits at the second position and the maximum lateral exhilaration allowed for the aircraft. In essence therefore, this patent discloses a system that establishes a flight path with intermediate way points that take into account certain constraints on the aircraft.
U.S. Pat. No. 5,086,396 (1992) to Waruazewski discloses an aircraft navigation system for use in determining routes in unfamiliar terrain or in terrain having hostile forces. The navigation system includes an inertial navigation system, a map of the terrain with elevational information stored in digitized format as a function of location, a typical energy managed or narrow beam altimeter, a display system and a central processing unit for processing data according to preselected programs. The system operates to maintain the true position of the aircraft with respect to the digitized map. A display of the map and the aircraft provide presentations useful to the navigation of the aircraft and enable the aircraft to engage in terrain following procedures using only the relatively difficult to detect altitude range finding apparatus as a source of emitted electromagnetic radiation. The navigation system, in conjunction with and information regarding hostile anti-aircraft facilities, can provide a display permitting an operator to determine a reduced risk flight path. This patent therefore discloses a navigation system that provides a means for enabling an aircraft operator to determine an appropriate route to avoid particular areas.
U.S. Pat. No. 5,087,916 (1992) to Metzdorff et al. discloses a method for navigating and updating navigation information by means of range imaging processing and a reference store that segmentizes range image data in order to obtain a particular pattern of type features for purposes of classifying particular types of objects across which the aircraft flies. The system extracts particular signature features including localized elevational jumps and determines the position of the aircraft by correlating a plurality of features and their spatial orientation to each other as extracted with corresponding stored reference information. This provides a maximum fit that is indicative of deviation of a flight from a flight path as identified by reference information. Thus this patent discloses a system that utilizes images and data base information containing terrain features to determine flight deviation from a predetermined path.
U.S. Pat. No. 5,187,667 (1993) to Short discloses a tactical route planning method for determining tactically sound paths or routes for vehicles from an initial position to a goal position across a piece of terrain. The system uses heuristic methods to select the most promising paths by sorting a list using a minimum estimated total cost value. If any of the list of paths reaches the goal it is selected. Otherwise new paths are generated by moving from the position at the end of the path to each of the adjacent terrain sections. Thus this patent discloses a method of obtaining a final path from a plurality of available paths.
U.S. Pat. No. 5,204,817 (1993) to Yoshida discloses a car mounted navigation system that uses map data in the form of polygons defined by roads of a predetermined rank or more of significance to connect a starting polygon containing a starting point to a destination polygon containing a destination with a chain of polygons adjoining at common sides of each pair of adjoining polygons and arranged between the starting and destination polygons to compute a plurality of routes extending from the starting point to the destination polygon. Each route can include a combination of sides of the chained polygons, the starting polygon and the destination polygon. A car operator selects an appropriate route from the computed routes. Thus this patent discloses a navigation system that divides an area into polygonal structures for use in generating one of a possible number of routes.
Generally, each of the foregoing applications discloses a system that is capable of plotting a navigation route. However, in each case the route can be plotted over an interval that is not time dependent. That is, the initial and final points remain fixed for a long period in comparison to the duration of an event. Time dependence, however, becomes an issue when in a dynamic situation such as determining a flight path for a missile in a tactical situation where the launch site for the missile is
U.S. Pat. No. 3,990,657 (1976) to Schott discloses a method and apparatus for reducing ballistic missile range errors due to viscosity uncertainties. Predictions of these errors provide a missile circular error probability in the form of a ballistic position error ellipse. The ellipse can be used to significantly improve performance by reducing error probability. This patent therefore discloses the use of ellipses in determining navigational information in a more dynamic scenario.
U.S. Pat. No. 4,044,237 (1977) to Cowgill et al. discloses a lifting body missile that is controlled by pitch and roll commands. A yaw auto pilot is caused to change in accordance with roll and estimated angle of attack input information. Command logic determines the polarity of the command signals to the auto pilot. This patent discloses onboard real-time apparatus for improving the trajectory of a missile.
U.S. Pat. No. 4,529,151 (1985) to Skarman discloses a method for steering an aerodynamic body in response to a body control variable signal. Specifically, the system responds to a signal value representing a line of sight angular rate and a signal value representing a body attitude angular rate. The two signal values are combined to form a signal value of an error angle. A difference error angle signal value is formed by an error angle measurement received from a homing device. The approximate error angle signal is fed back to the aerodynamic relationships in order to update the quantities of the relationships. This patent therefore provides a guidance system for moving a device from a launching point to a destination point in response to a target device that is moving.
In summary, each of these references discloses various approaches for guiding a vehicle from a starting point to a destination point. However, none of these references discloses any method or means for defining a route with intermediate way points set to avoid particular areas. Further, none of these references discloses any method or means for defining such a route in situations where the location of a starting point or distribution point may vary with time.
Therefore it is an object of this invention to provide a method for establishing a route through a plurality of way points positioned to avoid particular areas between a starting or launch point and a destination point.
Another object of this invention is to provide a method for establishing a route with intermediate way points between a starting or launch point and a destination point that enables the system to select the best possible route.
Still another object of this invention is to provide a method for establishing a route with intermediate way points between a starting or launch point and a destination point that enables the system to select a best possible route on a real-time basis.
Yet another object of this invention is to provide a method for establishing a flight path for a missile with intermediate way points between a starting or launch point and a destination point that enables the system to select a best possible flight path taking into account any constraints on the maneuverability of the missile.
A method according to this invention establishes at least one way point on a route for a steerable vehicle between a source point and a destination point that avoids at least one intermediate obstacle or area by defining first and second bearing lines from the source point to first and second tangents of each obstacle. Each of the bearing lines is extended an incremental distance beyond its tangent point with the area to define a potential way point. Thereafter each potential way point is converted to a way point for a route.
According to another aspect of this invention, a route is established for a missile between a launch point and a destination point that avoids at least one intermediate landmass or area. The method includes establishing a data base of landmasses in which each landmass is circumscribed with a polygon defined by a plurality of data points. After defining an initial source point and final way point, the method iteratively generates a plurality of routes between the initial source point and final way point. The final way point is the destination point unless destination is inside an obstacle (i.e., land mass boundary). During each iteration first and second bearing lines are generated from the source point to first and second tangents of the polygons surrounding each intermediate landmass. A potential way point relative to the tangent of each bearing line to the polygon is defined. Thereafter each potential way point is converted to an intermediate way point for the route and this way point is substituted as the source point. This process produces a number of routes. One of those routes is selected as a final route for the missile between the launching and destination points.